Liquid filled lens with variable focus have been proposed over the years for eyeglasses, cameras, camcorders, telescopes, binoculars, projectors as well as other machine vision applications. According to the lens operating mechanisms and liquid lens structures mentioned in several patents, the described lenses can be separated into two types. The first type is the liquid lens having a fixed volume of clear liquid which is sandwiched between a rigid lens or a planar substrate and a thin transparent elastic membrane, as described in U.S. Pat. Nos. 5,138,494 to Kurtin; 5,526,067 to Cronin et al.; 5,999,328 to Kurtin et al.; and 6,040,947 to Kurtin et al. By moving the periphery of the elastic membrane, the liquid inside the lens assembly is redistributed such that the curvature of the film is changed. The changed curvature of the liquid lens surface bounded by the elastic membrane can vary the optical power, also known as diopter, of the lens. The shortcoming of this kind of liquid lenses is that one can not easily keep the periphery of the elastic membrane parallel to that of the rigid lens or planar substrate during the distance change. Moreover, the operating system for tuning the focus is complicated.
The second type of liquid lens requires the pumping of liquid in or out the lens chamber to change the curvature of the elastic membrane surface, thus tuning the focus of the liquid lens as described in U.S. Pat. No. 5,684,637 to Floyd and U.S. Pat. No. 6,715,876 to Floyd. For the lenses operating by injecting or pumping liquid into the body of the lens, a complicated control system is usually needed; thus such lenses are bulky, expensive and sensitive to vibration. Similar to a conventional solid lens, a common feature of the abovementioned liquid lenses is that the diameter of the lens does not vary during the focus change.
Different from the above mentioned liquid lenses, another type of lens with variable focus obtained by changing its diameter was reported in U.S. Pat. No. 6,493,151 B2 to Schachar and is characterized as an elastically deformable lens. By making small changes in the equatorial diameter of the lens, the lens can be deformed by radial tension exerted in a plane generally perpendicular to the optical axis. The drawback of this kind of lens is that the control system used to change its diameter is complicated. The process for changing the focal length is quite complicated and sometimes inefficient.
Another kind of variable focus liquid lens is different from the above lenses; see for example, U.S. Pat. No. 6,369,954 to Berge et al. and U.S. Pat. No. 6,665,127 Bao et al. The focal length of the liquid lens is tuned by applying an external voltage. Usually the voltage applied to the liquid lens is very high (>200 volts) so that the power consumption is high. Power consumption is an important issue for portable devices as it is determined by battery life. The lens structure and the power supply system are complicated and expensive.
In the present invention, a tunable-focus liquid lens is adhesively attached to a circular periphery seal which looks like a conventional iris diaphragm with an impeller structure to impart movement and pressure to the fluid filled lens. The circular periphery seal can be operated mechanically or electro-mechanically to change the radius of the liquid lens. For example, if the radius is reduced, then the curvature of the elastic membrane becomes convex and a positive (or converging) lens is formed. On the other hand, if the radius is increased, then the membrane curvature becomes concave so that a negative (or diverging) lens is formed.